Ink jet printing, in which pressurized liquid streams are used, requires that the stream be broken up into a regular succession of drops of uniform spacing and size. This breakup is accomplished by creating a succession of perturbations or disturbances in the liquid filament as it issues from an orifice in a nozzle. In the past, perturbations have been created by modulating either the ink velocity or pressure within the chamber preceding the orifice.
Velocity modulation is generally brought about by connecting an electromechanical transducer (usually a piezoelectric crystal) structurally to the surface in which the exit orifice is mounted. Energization of the transducer causes the orifice surface to oscillate along the longitudinal axis of the issuing stream at the applied drive frequency which, in turn, creates inertially produced pressure perturbations of the ink in the region of the orifice. This perturbation initiates drop generation in the liquid filament issuing from the orifice. An example of this type of perturbation is shown in U.S. Pat. No. 3,512,172.
Pressure modulation is usually accomplished by locating an electromechanical transducer (again usually a piezoelectric crystal) either in the liquid chamber or surrounding the chamber. Energization of the transducer produces standing waves acting on the ink within the chamber to produce pressure perturbations on that ink. In the region of the nozzle orifice, these perturbations again initiate the formation of drops in the liquid filament issuing from the orifice. U.S. Pat. No. 3,281,860 illustrates pressure perturbation.
In each of these methods of modulation, reflected waves are difficult to control, requiring tight component tolerances and associated high cost. In addition, ink supply chambers are at times difficult to construct which would maintain the fidelity required between the chamber compliance and applied transducer signals. Also, the presence of air bubbles in the ink adversely affect compliance. A further difficulty is due to reflected waves within the supply chamber which cuases irregular modulation of the stream. These difficulties result in nonuniform drop spacing or size and permit the generating of an excessive number of satellite drops over the applied frequencies and signal amplitudes of the transducers.